This invention relates to improvements in or relating to vacuum belt filters. It relates in particular to a suction box for such a filter and to a method of operation of the filter.
Vacuum belt filters normally have an endless belt, with a central longitudinal opening, which is displaceable over a suction box. The suction box is elongate and is disposed about the opening. The belt further has transverse channels along its upper surface upon which a filter cloth is provided. When a suction pressure is provided in the suction box, filtrate is drawn from material that is to be filtered, and which is carried on the filter cloth, through the opening in the belt into the suction box.
However, due to the suction pressure, the belt is pulled down against the upper edges of the suction box. The frictional engagement between the lower surface of the belt and the upper edges of the suction box results in undue wear of the belt and the suction box, heating of the belt, and drag on the belt which requires extra energy to displace the belt over the suction box.
Further, there must be an adequate seal between the edges of the suction box and the belt, so that air from the atmosphere is not drawn between the lower surface of the belt and the edges of the suction box, thereby decreasing the efficacy of operation of the filter.